Thermally stable beta alloys of titanium-tin alloys



United States Patent No Drawing. Application November 1, 1952,

Ni 18,3 9 s ams- (GI-75:175-5) This invention pertains to titanium base alloys containing one or more beta promoters or stabilizers, together with tin in amount such as to function as a retardant of Phase han e or eutsc c dec mpos o du in aging f the alloy.

As is known, the metal titanium in the pure state, is capable of existing in either of two allotropic forms. Below a temperature of about 885 C. or 1 525 F., it assmiles a close-packed hexagonal microst'ructure known as .19 3112119 phase, While at this temperature and above it assumes a body-centered cubic structure known as the beta phase.

Certain substitutional alloying additions to the titanium base'metal, among which maybe mentioned aluminum,

iii'dium; antimony, bismuth, lead arid'silver," as well as the interstitials carbon, oxygen" and nitrogen, tend to stabilize the alpha phase. addition tin, likewise in general fune'tions as an alpha stabilizer, ancl'heretofore has been "exclusively regarded as such.

Other substitutiona l alloying elements, when added in progressively increasing quantities, stabilize the beta phase at progressively lower temperatures, until a mixed alphabeta for s-tablEall-beta microstructure is obtained at norai or t s h te er tu es; Qir'th c 'phase'nndeire goes a eutectoi'cl reaction, depending on the'character and amount of the beta stabilizers added. f

Speaking in broadest terms, the beta stabilizers are h i st m ia a' l'qyins' Mn, Mo, Cr, Fe, Cu, VQZrIWICb, Ta, C0 andNil Silicon andberylliurn may also be considered as beta stabilizing elements, but'their solubilities iri'titanium are relatively small, so that it is equally proper to consider them ascompo'und-formiflg filffients. Within this'b'road category, however, only certain of the elements mentioned are suitable for producing mixed-phase alpha b'et'a alloys, or stable beta alloys. 'Theise ar'eThe elements which have beta-isomorphous diagrams, crWhichli ave beta-eutectoidciagrams such that the" decomposition of the beta phase into eutectoid is 'so sluggish that thealloys behave'like those a beta-isomorphous system. "The beta'stabilizing elements of this type are 'Nin, Mo, Cr

Fe, V, Cb, W and Ta.

'Zirjconium is a beta promoter or stabilizer in the sense i that the lowest temperature at whichthealloy'the'reof with titanium is entirely beta, becomes progressively lower with increasing amounts of zirconium," until 5 en peraturje is reached at which'this so-called beta transus temperature startsto'increase again with increasing additions of zirconium. Additionsof up to 20 ?0 zirconium have proved effective in this respect. While zirconium thus lowers the transformation temperaturebf titanium,

titanium, does not fit into the last-mentioned group of beta stabilizing elements, because the beta phase stabiingembrittlenient of many such beta ice lized by copper always decomposes into pro-eutectoicl and elite oid products, and t I same is generally "true with respect to cobalt, nickel, silicon and "beryllium, above listed under the bioad category of beta stabilizers. Copper, however, "a useful addition' when presentas' a minor alloying element, for e em lar-1pm a few percent, inalloys containing larger" amounts of'othe'r' beta stabilizing elements, within the narrow groupof elements last mentioned above sihce; in these low concentrations and in the presence 'off such oth rbe'ta "stabilizing elements; the tendency of copper to decompose into eut'ectoid this i minimized or entirely eliminated.

' Substantially pure and ductile tallic titanium may be produced t o s dera l are th -s l di d i processdes'cribe'd in UZS. Patent 1,671,213 toVan Arkel; while ductile titanium of commercial purity can be produced more cheaply by the magnesium reduction of titanium tetrachloride by the process described in U. S. Patent 2,205,854 to Kroll. Both procedures, particularly the latter, result in some contamination of the titanium metal with one or more of the interstitials, carbon, oxygen and nitrogen. But since, as noted above, these are all alpha promoting or stabilizing elements, the resultant titanium metal obtained, has at room temperatures a single phase, all-alpha microstructure.

The all-alpha, all-beta and mixed alpha-beta alloys of titanium have their respective advantages and disadvantages. Generally speaking, the alpha alloys provide good all around performance, having good weldability, and being -strong aiid resistant to oxidation, both cold and hot, but are sbmewhat inferior as to ductility. The all-beta aIIoysIOn thBther hand, have excellent bendability and ductility, are-strong both hot and cold, but are somewhat vulnerabletoatmospheric contamination, particularly at elevated temperatures. The mixed alpha-beta alloys provide" a ciompi omise performance as between all-alpha and all-beta allbys, being strong when cold and warm, but" weak when hot, while possessing good bendability and ductility, with a moderate degree of resistance to atmospheric contamination.

" Investigations have shown that there are relatively few all-beta titanium base alloys which remain stable on aging at eleyated temperatures. The vast majority would morecorrectly be classified as unstable beta alloys, in tha tthey"have an all-beta microstructure on rapid cooling ofciuenching from the beta field, but which on subse'guent a'g'ir gbr hot working, at temperatures below 1625? F' or 885? C., transform in greater or lesser degree into the alpha phase or into eutectoid decomposition products or into both. This phase transformation tends toembrittle the alloy, so much so for many analyses as to entirely destroy ductility for fabrication purposes. Nowil'have'dis'covered in accordance with the present invention "that this phase transformation and accompanyalloys is greatly minimizedby the addition of tin in amounts critically related' to thefa'ggregate content of the beta promoting elements presentih the alloy. "Althoughfas" above stated, tin has heretofore been regarded exclusively as an alpha stabilizing element, I have discovered inlaccordance with my invention, that curiou'sly enough, wh en added in appropriate amounts to beta alloys or character aforesaid, tin apparently functions as a beta stabilizing element, at least to the extent of greatly retarding 'or eliminating the conversion of the fb'eta phaseftdalpha and/or eutectoid decomposition prodshrouds, high performance aircraft skins, etc.

I have determined experimentally, as evidenced by the bend duc- 100 Hts. at 500 F.

m BBBB .44313 J BB BsB sB sBMmm sBB La a" 45466 3 5 571 5 1&2 4 7 2 elements presference to these flective. On the other thing on the order On the other hand,

in general to be de 100 Hrs. at 750 F.

1 .B B BBBBB B BB B BBBB BBB BB BBBBBB B B B B B BB B 55 54333 3 6 6 4 5775 27567 6 6 7 7 e of about 12 to 17%, little additions as low as 2%, while 50 76 7 7 16 774 79 6 mm m m 77M 66 we msm7eneee weemmsmmwwwwwmmwflwwwm mwmwm n n a Be .333 a 3 A h JAB B B we 33 s .1 s B 1 l3 2 5 32 63 81 6 7 7 4 (a) hardness changes, and (b) bend TABLE I base alloys resent in the alloy, something under 5% tin and As Rolled and 24 Hrs. at

Annealed Bend '1 Ba Bend '1 Ba Bend T Ra Bend T Re 14.661 11629515 6681 5411 731 4 4 24694 2171187215635182612 5860 I 4 ,1543 1 24L1 12 L1 66 26332 4;. 6 6 4-L3 2 2 2L 2 L3 4- with an aggregate content of some of beta transus temperature lowering ent,

increase in hardness without drastic loss of is considered a promising indication for the heat elements p ranging down to about 2% is most e hand,

5 as much as 10% or more of tin may be required for most effective thermal stabilization. for alloys containing an aggregate of beta promoters within the preferred rang benefit is gained from tin 10 additions as high as 10%, appear mental.

In the test results set forth in Table I below, in support of the above, two criteria for thermal stability have been employed, ductility changes, with aging. With re data, tility,

tin adupwards lowering Effect of tin additions on thermal stability of beta titanium ion, Percent (Balance Titanium) from about. 3 to timum effect occurring in general at about are found to Composlt n n u e m n 0 1 u .MO m m MM m a u n a "m r mu n n n m u :1... IOOn 0 u. F ZZ .00 5 77 n MM m Jur m lnm N Mss p 00 wwzzcc .r 7 M55 1 55mm a ,5, am 55 new 6 6 mm muli lm n u n n n u u n a "0 u u n a 050 510504 arkedly improved and preferably about 12 to 17%, of beta promoting or beta transus temperature lowering elements.

tin additions as low that in general the thermal stability of beta alloys of titanium is m by additions ase alloys containing 3 test results presented below,

of tin in amounts ranging 7%, with an op 5%. This represents the preferred range of the ditions for most effective thermal stabilizing action, an particularly as applied to titanium b an aggregate of not over about 20 a,

For certain beta alloys of titanium, as about 2%, and as high as about 10% impart noticeable or substantial thermal stabilization. Within this broad range smaller tin additions are most etfective in the alloys containing higher aggregate contents of beta promoters and vice versa. Thus, with of in aggregate of beta transus temperature 1 B -completely brittle. .13 in column A Is, of course, B in all columns.

treatable beta alloys. It has been found, however, that any hardness increase by aging aloneto Rockwell fA 70 or above, is almost invariably associated with more or less complete embrittlement. In Table I, the test data of column A gives the bend ductility and Rockwell A hardness, of each alloy of the analysis shown, in the condition resulting from rolling at 1400 F. to an intermediate gauge followed by cleaning and further rolling at 1300 F. final gauge, and thereupon holding at 1300 F. for one-half hour and furnace cooling to 1100 F., and finally air cooling to room temperature. Column B gives the bend ductility and Rockwell A hardness for the specimens as prepared under A, and thereupon aged for 24 hours at 750 F.; while columns C and D give data corresponding to column B, except that the aging is carried out for 100 hours at 750 F. for column C and for 100 hours at 500 F. for column D.

Referring to the data of- Table I, it will be observed that, in general, the beta alloys which are embrittled and unduly hardened on aging in the absence of tin, are converted into thermally stable alloys by appropriate tin additions and retain adequate ductility and low hardness under the various aging conditions set forth. The thermal stabilizing action of the tin varies somewhat with the specific beta promoting elements present. With reference to the binary alloys shown, tin is quite efiective in imparting thermal stability to those in which the beta promoting element comprises manganese, and possibly zirconium or vanadium, but offers no material improvement as regards those in which the beta promoter is molybdenum, iron or chromium. On the other hand, it is quite generally true that the tin addition ofifers a great improvement with respect to practically all of the ternary and quaternary alloys such as the manganesechromium, manganese-molybdenum and chromiummolybdenum ternaries. Also improvement is shown in certain of the ternaries containing iron, particularly Where the iron is present in amounts not exceeding about All of the quaternary alloys are materially improved as to thermal stability by the tin additions, the majority of those generally being embrittled on aging in the absence of tin, but in maintaining adequate ductility with low hardness under the most severe aging conditions when tin is present in appropriate amounts.

From this the generalization may be drawn that a multiplicity of beta stabilizers in the alloy along with tin appears to be generally advantageous, provided that no one of the beta promoters is present in excessive or preponderant amount as compared to the others, except possibly manganese.

The test results of Table I further establish that the alloys according to the invention which are found to be most stable thermally are those containing about 15% in aggregate of a multiplicity of beta transus temperature lowering elements, together with about 5% tin.

Since the elevated temperature range within which titanium possesses advantages in use over other materials, is about 400-800 F., the aging tests of Table I were carried out within this range.

The alloys of the invention may be made by melt casting in a cold mold employing an electric arc and an inert atmosphere, or may be produced in other ways in which the alloy is rendered molten before casting.

My experiments on high beta, titanium base alloys, indicate that while alpha separation resulting from overaging does not necessarily impair ductility seriously, the same is not true with respect to eutectoid decomposition, which results only in increasing embn'ttlement. Hence, in seeking a stable beta alloy, the advantage gained in beta transus temperature lowering by adding more and more of the beta stabilizers, is oflset by the increasing tendency toward eutectoid decomposition. In this connection, the noneutectoid beta stabilizers, such as V, Cb, Ta and Mo are 6 either too expensive, rare or heavy to be employed alone. For this reason, tin is a particularly valuable addition to the beta alloys of titanium. As shown above, t-in is not a beta stabilizer in the sense that V, Cb, Ta, etc., are. The latter lower the equilibrium beta transus temperature, while tin does not. .As stated, tin has heretofore been considered as an alpha stabilizer. But with respect to the alloys of the present invention, although tin confers sluggishness to the beta decomposition, it does not, itself, form a eutectoid with titanium. Hence the effect of adding tin to the alloys of the invention is that of adding a true beta transus temperature lowering element, while at the same time suppressing eutectoid decomposition. In this respect it stands in marked contrast to the beta transus temperature lowering elements, since the latter other than the expensive, rare or heavy ones, increase the tendency to eutectoid decomposition.

It is thus shown that tin, normally an alpha stabilizer, nevertheless renders beta alloys sluggish in decomposition. Also, that the addition of tin provides etfectively stable beta alloys at lower aggregate contents of the beta promoters which produce eutectoid decomposition, than is obtainable in the absence of tin. The tin additions also effectively thermally stabilize many of the beta analyses which would otherwise be unstable on aging.

It is to be understood that the beta alloys in accordance with the invention may also contain one or more of the alpha promoters above listed, provided they are not present in suflicient amount to destroy the beta characteristics of the alloy.

In the appended claims, by the expression beta promoting elements is meant an element of the group molybdenum, vanadium, columbium, tantalum, zirconium, chromium, manganese, iron, tungsten, cobalt, nickel, copper, silicon and beryllium.

I claim:

1. A titanium-base alloy consisting essentially of: about 10 to 20% of at least one beta-promoting element, about 2 to 10% tin, and the balance substantially titanium, characterized by high thermal stability and retention of ductility on aging in the temperature range of about 400 to 800 F.

2. A titanium-base alloy consisting essentially of: about 10 to 20% of at least two beta-promoting elements, about 2 to 10% tin, and the balance substantially titanium, characterized by high thermal stability and retention of ductility on aging in the temperature range of about 400 to 800 F.

3. A titanium-base alloy consisting essentially of: about 10 to 20% of at least three beta-promoting elements, about 2 to 10% tin, and the balance substantially titanium, characterized by high thermal stability and retention of ductility on aging in the temperature range of about 400 to 800 F.

4. A titanium-base alloy consisting essentially of: about 10 to 20% of at least one beta-promoting element selected from the group consistingof molybdenum, vanadium, columbium, tantalum, zirconium, chromium, manganese, iron, tungsten and copper, about 2 to 10% tin, and the balance substantially titanium, characterized by high thermal stability and-retention of ductility on aging in the temperature range of about 400 to 800 F. 5. A titanium-base alloy consisting essentially of:

about 10 to 20% of at least two beta-promoting elements selected from the group consisting of molybdenum, vanadium, columbium, tantalum, zirconium, chromium, manganese, iron, tungsten and copper, about 2 to 10% tin, and the balance substantially titanium, characterized by high thermal stability and retention of ductility on aging in the temperature range of about 400 to 800 F.

6. A titanium-base alloy consisting essentially of: about 10 to 20% of at least three beta-promoting elements, selected from the group consisting of molybdenum, columbium, tantalum, zirconium, chromium, mant i References Cited in the file of this patent UNITED STATES PATENTS Re. 24,013 I Jaffee May 31, 1955 Methe Jan. 25; 1955 

1. A TITANIUM-BASE ALLOY CONSISTING ESSENTIALLY OF: ABOUT 10 TO 20% OF AT LEAST ONE BETA-PROMOTING ELEMENT, ABOUT 2 TO 10% TIN, AND THE BALANCE SUBSTANTIALLY TITANIUM, CHARACTERIZED BY HIGH THERMAL STABILITY AND RETENTION OF DUCTILITY ON AGING IN THE TEMPERATURE RANGE OF ABOUT 400 TO 800* F. 